Two-way radios are typically designed with a robust amount of gain in their amplifier stages. As is well known in the art, one drawback of providing too much gain occurs when multiple communication systems are operated in close proximity to one another. The radio frequency (RF) gain stages of the radio receiver can both provide gain but can also work to enhance interference. Generally, the cause of this problem stems from intermodulation distortion (IM) and adjacent channel interference which degrade radio performance in the form of poor radio reception. Intermodulation distortion interference occurs from adjacent channel interference then mixes with other RF signals to produce an unwanted RF signal on or near the desired frequency of operation. This type of interference is becoming very common as radio spectrum becomes more crowded with differing types of users, RF signal power levels and modulation schemes all attempting to fit into a finite space.
In the past, one common way to help the receiver reduce this type of interference has been through the use of an attenuator. The attenuator is a circuit that may be inserted between the antenna of the radio receiver and the RF amplifier circuitry in order to reduce the amount of RF energy reaching the receiver. This RF energy takes the form of on-channel signals as well as off-channel interference appearing on the desired frequency to interference with the desired on-channel signals. As a general rule since the intermodulation product is a third order non-linear expression, every one decibel (dB) of attenuation that is switched in circuit provides a three dB reduction in the amount of intermodulation interference in the radio receiver.
One problem associated with this type of approach is that not all transceivers have an integrated attenuator for use with the receiver. Any external attenuation would not only be inconvenient to use but also would add extra weight and expense to the operation of the device. Accordingly, the need exists to provide a system and method that would enable existing circuitry used within a radio transceiver to act as an attenuator when needed. This would work to ultimately optimize the performance of the radio receiver by enabling the user to accurately receive various signal levels of incoming information while having the ability to enable an internal attenuator for situations where adjacent channel interference is present.